Portable electronic device are supplied power for device operation by a mobile power source, such as a battery. A typical battery pack assembly comprises a battery cell, such as Lithium-ion (“Li-ion”) cell for example, having a positive terminal and negative terminal. One or more safety protection devices may be coupled between the terminals and external contacts that interface with the electronic devices to effectively disconnect the battery cell from the device. For example, a positive temperature coefficient (“PTC”) device operates as a thermally activated fuse by increasing in resistance when its temperature exceeds a threshold. This high temperature can be caused by high current levels, high ambient temperatures or a cell that is heating due to internal short circuits.
In addition to a PTC, Li-ion cells based on cobalt chemistry typically employ a protection circuit module (“PCM”) that actively disconnects the cell from the load under the certain conditions, such as excessive voltage, excessive current, low voltage, excessive temperature, among others.
A challenge in any battery pack assembly design is the need to incorporate safety protection devices in a compact form, particularly in view of increased customer demand for smaller electronic devices. A plastic housing normally encompasses the package and therefore adds extra thickness to the package, typically on the order of several millimeters.
Some battery packs designed to have reduced sizes result in other undesirable shortcomings, such as reduced reliability or increased costs. For example, in a carefully designed pack using thin walled plastics that require expensive injection molding techniques (such as low pressure molding (“LPM”) or insert molding) and equipment, this added thickness can be reduced to less than a millimeter, but the associated manufacturing cost is significantly increased. Accordingly, there remains a strong need in the art for a compact mobile power source and method of assembly thereof which addresses one or more of the deficiencies in existing battery pack assemblies.